Method and apparatus for forming resist pattern

ABSTRACT

A method of forming a resist pattern on a substrate, comprises the steps of: forming a resist film on the substrate, supplying a developing solution onto the resist film, submerging the substrate and the resist film formed thereon in a rinsing liquid kept in a rinsing tank, and applying ultrasonic vibration to the rinsing liquid to rinse the developing solution from the resist film submerged in the rinsing liquid.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method and apparatus forforming a resist pattern on a substrate used in semiconductorfabrication processes and a resist pattern used for a photomask such asa reticle.

[0002] Recently, chemically amplified resist patterns are formed bymeans of the lithographic technique utilizing the KrF excimer laserexposure. Especially, negative resist, which provides unexposed portionsthat dissolve in developing solution, is important for super-resolutiontechniques (Levenson phase shift masks).

[0003] However, if chemically amplified negative resist is used toproduce a line-and-space pattern 21, for instance, microbridges 22 thatpartially connect adjacent portions of the pattern are readily formed,as shown in FIG. 1, reducing yields.

SUMMARY OF THE INVENTION

[0004] An object of the present invention is to provide a method andapparatus for forming a resist pattern on a substrate, which suppressesgeneration of microbridges.

[0005] According to an aspect of the present invention, a method offorming a resist pattern on a substrate, comprises the steps of: forminga resist film on the substrate; supplying a developing solution onto theresist film; and submerging the substrate and the resist film formedthereon in a rinsing liquid kept in a rinsing tank; and applyingultrasonic vibration to the rinsing liquid to rinse the developingsolution from the resist film submerged in the rinsing liquid.

[0006] According to another aspect of the present invention, anapparatus for forming a resist pattern on a substrate comprises: arinsing tank which keeps rinsing liquid for rinsing developing solutionremaining on a resist film formed on the substrate; and an ultrasonicvibration mechanism which applies ultrasonic vibration to the rinsingliquid kept in the rinsing tank.

BRIEF DESCRIPTION OF THE INVENTION

[0007] The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

[0008]FIG. 1 is a perspective view showing microbridges that partiallyconnect adjacent portions of the pattern;

[0009]FIGS. 2A to 2F are diagrams showing the steps of a process forforming a resist pattern according to a first embodiment of the presentinvention;

[0010]FIG. 3 is a perspective view showing a resist pattern free frommicrobridges;

[0011]FIGS. 4A and 4B are diagrams showing schematic views of a patternformed through the rinsing step in which ultrasonic vibration is applied(the first embodiment) and a pattern formed through the conventionalmethod;

[0012]FIG. 5 shows the relationship between light exposure (mJ/cm²) andpattern dimensions (μm) in the process for forming a resist pattern,depending on the ultrasonic processing; and

[0013]FIGS. 6A to 6E are diagrams showing the steps of a process forforming a resist pattern according to a second embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0014] Further scope of applicability of the present invention willbecome apparent from the detailed description given hereinafter.However, it should be understood that the detailed description andspecific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications will become apparent to those skilled in the art fromthe detailed description.

[0015] First Embodiment

[0016]FIGS. 2A to 2F are diagrams showing the steps of a process forforming a resist pattern according to a first embodiment of the presentinvention.

[0017] In the first embodiment, a negative resist film 2 is first formedon a substrate 1 through spin coating or another method, as shown inFIG. 2A. The substrate 1 is a silicon substrate, for instance. Thenegative resist film 2 is made of chemically amplified negative resist,is about 0.5 μm thick, and is prebaked (PB) at about 110° C., forinstance. However, the materials, thickness, and processing temperatureof the substrate 1 and the negative resist film 2 are not limited tothose described above. In addition, a positive resist film may be usedinstead of the negative resist film 2.

[0018] Next, as shown in FIG. 2B, the negative resist film 2 is exposedto light passing through the mask 3 having a desired pattern of openings3 a. The light exposure amounts to about 23 mJ/cm², for instance. Theshape of the mask is not limited to the one shown in the figure, and thelight exposure is not limited to the value indicated above.

[0019] Then, as shown in FIG. 2C, the post exposure bake (PEB)processing is performed. The PEB processing is heat-up processing atabout 105° C. The temperature of the PEB processing may be differentfrom the value indicated above.

[0020] Next, as shown in FIG. 2D, developing solution is supplied toremove the unexposed portions of the negative resist film 2. Thedeveloping solution may be supplied by directing jets of developingsolution through a nozzle or by submerging the substrate in thedeveloping solution, for instance. The developing solution is, forexample, a 2.38% tetramethylammonium hydroxide (TMAH) developingsolution, which is an alkaline developing solution. The developing timeis about 60 seconds, for instance. However, the developing solution anddeveloping time are not limited to those indicated above.

[0021] Then, as shown in FIG. 2E, the substrate 1 and the developednegative resist film 2 are submerged in pure water 5, which is therinsing liquid kept in a rinsing tank 4, then ultrasonic vibration isapplied to the pure water 5. The frequency of ultrasonic vibrationranges from 40 kHz to 50 kHz, for instance. The ultrasonic generator 6is built in the wall structure of the rinsing tank (container) 4 filledwith the pure water 5. The ultrasonic generator 6, however, may beprovided inside or outside the container 4 and may also be disposed on atable on which the container 4 is placed. The ultrasonic frequency andultrasonic processing time can be changed as desired by means of acontroller (not shown).

[0022] Then, as shown in FIG. 2F, the substrate 1 having the negativeresist film 2 is taken out of the rinsing liquid and dried. In thedrying step, the spin dry method is used, for instance.

[0023] As has been described above, the generation of microbridges canbe suppressed through a quick and convenient method such as ultrasonicprocessing during rinsing, according to the first embodiment. As aresult, a resist pattern free from microbridges can be formed, as shownin FIG. 3. Moreover, by combining the ultrasonic processing unit and thepure water processing unit into a single unit, the throughput can beimproved.

[0024]FIGS. 4A and 4B are diagrams showing schematic views of a patternformed through the rinsing step in which ultrasonic vibration is applied(pattern formed according to the first embodiment) and a pattern formedthrough the rinsing step in which no ultrasonic vibration is applied(pattern formed by the conventional method). In the experiment forforming the pattern shown in FIG. 4A, the silicon substrate is appliedwith a layer of commercially available chemically amplified negativeresist of about 0.5 μm thick, a resist film is formed through the PBprocessing at about 110° C. and exposed to light of about 23 mJ/cm²,then the PEB processing is performed at about 105° C. In the developingstep, a 2.38% TMAH developing solution is used as the alkalinedeveloping solution, and a developing time of about 60 seconds is taken.In the rinsing step, the wafer is submerged in the pure water, andultrasonic vibration of about 40 kHz to 50 kHz is applied. The comparedexample shown in FIG. 4B is formed by applying a layer of commerciallyavailable chemically amplified negative resist of about 0.5 μm thick ona silicon substrate, forming a resist film through the PB processing atabout 110° C., exposing to light of about 23 mJ/cm², and performing thePEB processing at about 105° C. In the developing step, a 2.38% TMAHdeveloping solution is used as the alkaline developing solution, and adeveloping time of about 60 seconds is taken. In the rinsing step, thewafer is submerged in the pure water, and no ultrasonic vibration isapplied. This experiment proves that the generation of microbridges issuppressed by performing ultrasonic processing during rinsing.

[0025]FIG. 5 shows the relationship between light exposure (mJ/cm²) andpattern dimensions (μm) in the process for forming a resist pattern,depending on the ultrasonic processing. In the figure, white trianglesrepresent data taken when no ultrasonic processing is performed inrinsing (compared example shown in FIG. 4B) while black circlesrepresent data taken when ultrasonic vibration is applied in rinsing(example shown in FIG. 4A according to the first embodiment). Thisexperiment proves that the light exposure margin, which has a greateffect on manufacturing yield, has also increased according to the firstembodiment.

[0026] In the description above, the ultrasonic processing is performedin rinsing only, but the ultrasonic processing may be performed duringthe developing step.

[0027] Second Embodiment

[0028]FIGS. 6A to 6E are diagrams showing the steps of a process forforming a resist pattern according to a second embodiment of the presentinvention. With the second embodiment, a process for producing aphotomask such as a reticle is described.

[0029] First, as shown in FIG. 6A, a negative resist film 12 is formedon a quartz substrate 11 through spin coating or another method, andthen the PB processing is performed. Then, as shown in FIG. 6B, theelectron beam (EB) lithography technique is used to irradiate thenegative resist film 12 with a dose of electron beam 13, and the PEBprocessing is performed. Next, as shown in FIG. 6C, developing solutionis supplied, and unexposed portions of the negative resist film 12 areremoved. Then, as shown in FIG. 6D, the quartz substrate 11 and thedeveloped negative resist film 12 are submerged in pure water 5, whichis a rinsing liquid kept in the rinsing tank 4, and ultrasonic vibrationis applied to the pure water. Next, as shown in FIG. 6E, the quartzsubstrate 11 having the negative resist film 12 is taken out of therinsing liquid and dried.

[0030] As has been described above, the generation of microbridges canbe suppressed by a quick and convenient method such as the ultrasonicprocessing during rinsing, according to the second embodiment.Consequently, a mask made from a resist pattern without microbridges canbe formed, as shown in FIG. 3. The mask with few microbridges can beused for forming a 4-times reticle, for optical proximity correction(OPC), and for the like.

[0031] The second embodiment is the same as the first embodiment exceptfor the items described above.

[0032] The invention being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of following claims.

What is claimed is:
 1. A method of forming a resist pattern on a substrate, comprising the steps of: forming a resist film on the substrate; supplying a developing solution onto the resist film; and submerging the substrate and the resist film formed thereon in a rinsing liquid kept in a rinsing tank; and applying ultrasonic vibration to the rinsing liquid to rinse the developing solution from the resist film submerged in the rinsing liquid.
 2. The method of claim 1 , wherein said step of applying ultrasonic vibration is conducted by applying ultrasonic vibration to said rinsing tank.
 3. An apparatus for forming a resist pattern on a substrate comprising: a rinsing tank which keeps rinsing liquid for rinsing developing solution remaining on a resist film formed on the substrate; and an ultrasonic vibration mechanism which applies ultrasonic vibration to the rinsing liquid kept in said rinsing tank.
 4. The apparatus of claim 3 , wherein said ultrasonic vibration mechanism applies ultrasonic vibration to said rinsing tank. 